Red tide damages oxygen levels in the water which affects marine life.  If one consumes fish or shellfish that has been affected by red tide, there will be tingling in the lips, tongue and face.  There could also be difficulty breathing, dizziness and vomiting.  The symptoms usually appear within 30-60 minutes after ingestion.  The preferred basic treatment is to induce vomiting by administering warm salt water (from a clean source) and seek the attention of a doctor immediately.  The best way to know if red tide is in effect for Banderas Bay is to do a simple Google search:  red tide in PV (and the month and year you are inquiring about).  The local papers will report it.